Structure of the shell wall of Raskiniella plana (subclass Spirillinana)

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Abstract

Among the four classes of multicameral foraminifera with a secretive calcareous shell wall, the ultrastructure of the wall is known in three of them – in the classes Rotaliata Mikhalevich, 1980, Miliolata Saidova, 1981 and Nodosariata Mikhalevich 1992. It was believed that the wall of Spirillinata Mikhalevich, 1992 was formed by one or more large crystals. In this study, it was found that in one of the typical representatives of this class, Raskiniella plana (previously classified as Spirillina plana, Wiesner, 1931), the entire shell is formed by amorphous (not crystalline) CaCO3. Previously, amorphous calcareous skeletons were known in some unicellular algae and multicellular eukaryotes, but in foraminifera, the skeleton of the entire adult shell, completely formed by the amorphous form of CaCO3, was discovered for the first time.

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About the authors

V. I. Mikhalevich

Zoological Institute of the Russian Academy of Sciences

Author for correspondence.
Email: mikha07@mail.ru
Russian Federation, St. Petersburg

References

  1. Loeblich A.R., Jr., Tappan H. Foraminiferal genera and their classification. Univ. California // Los AngelesVan Nostrand Company. N.Y. Vol. 1, 2. P. 1–970.
  2. Martignier, A., Pacton M., Filella M., Jaquet J.-M., Barja F., Pollok K., Langenhorst F., Lavigne S., Guagliardo P., Kilburn M. R., Thomas C., Martini R., Ariztegu D. // Intracellular amorphous carbonates uncover a new biomineralization process in eukaryotes. 2016.
  3. Mikhalevich V.I. The phylum Foraminifera d’Orbigny, 1826. In: Alimov A.F. (ed), Protisty: Rukovodstvo po Zoologii, pt. 1. Nauka Publishers, St. Petersburg. P. 533–623. With English Summary P. 611 – 616. Михалевич В.И. Тип Фораминиферы d’Orbigny, 1826. В: Алимов А.Ф. (Ред), Протисты. Руководство по зоологии, ч.1. Наука, Санкт-Петербург. С. 533–623. Резюме на английском С. 611–616.
  4. Mikhalevich V.I., Kaminski M.A. // New taxa of the superorder Spirillinoida (Foraminifera). // Zoosystematica Rossica, 2024, Vol. 33. № 1. P. 48–64.

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2. Fig. 1. Outer wall of the shell of Raskiniella plana Mikhalevich et Kaminski, 2024 (German vessel Polarstern, Antarctica, 1996, station 2, Weddell Sea, 71o 18’ 60”, near Cape Norvegia, depth 181–253 m, 22.02.1996. A – view from the dorsal side of the shell with a network of peripheral canals turning into radial canals on the dorsal side (x300); B – shell wall between radially running canals, a – not destroyed, b – destroyed (x1600); C–E – destroyed wall from the upper side of the radial canal and between the canals, destroyed fragments of the wall of various shapes are visible, including cubic, triangular and irregularly shaped (C, D – x1500, E – x2000).

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3. Fig. 2. Inner wall of the Raskiniella plana shell. A (x2000) – broken apertural end allowing the inner wall to be seen, B – enlarged part of A: note the predominant elongated bead-like canals (er) and less frequent wide bead-like canals (wr), as well as the tubular (t) canals, r – cross-section of the radial tubular canals on the upper side of the shell, f – wall fragment; C – tubular canals of the inner wall on the umbilical side of the shell, D – radially running microcanals (arrow) of the thin dense superficial layer on the dorsal side of the shell.

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4. Fig. 3. A, B – elongated bead-like canals of the inner wall of the dorsal side of the shell, prevailing in the inner wall of this side in Fig. 2 B, C – E – microcanals as the smallest structural elements of the Raskiniella wall. A, B – part of Fig. 2 (A – enlarged), C – fragment of the broken wall of Fig. 2, enlarged: B – larger wide bead-like canal (wr) (left) among microcanals (mc) – right; D – part of Fig. 2, microcanals, enlarged; E, F – microcanals of part of the superficial wall (E – part of F, enlarged), ca – cross-sections of larger canals intersecting the wall.

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5. Fig. 4. Stages of formation of wall elements. A (x 2870) – vitreous substance during restoration of the radial canal of the last whorl of the tubular chamber. B – fig A, enlarged: formation of a wide beaded canal (wrc) (lower left corner), elongated beaded canals (lower right corner) and multiple needle-shaped microchannels (mc), C (x2870) – a later stage: formation of a smooth upper wall of the radial canal from needle-shaped and other microchannels (dc); D – part of figure C (enlarged).

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Presented by Academician of the Russian Academy of Sciences S.V. Rozhnov


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